1. Field of the Invention
The present invention relates generally to read heads for use in magnetic heads for hard disk drives, and more particularly to a read head which includes a multi-layer magnetic hard bias element.
2. Description of the Prior Art
Magnetic heads for hard disk drives typically include a read head portion and a write head portion. In a commonly used read head, a magnetoresistive read sensor layered structure is located in a read region, while a magnetic hard bias element and an electrical lead element are located in each of two side regions. The sensor typically comprises an antiferromagnetic pinning layer, a pinned magnetic layer, a nonmagnetic spacer layer, a free magnetic layer, and a nonmagnetic cap layer. The hard bias element typically comprises a nonmagnetic seed layer and a hard-magnetic biasing layer.
In such magnetic heads the free magnetic layer is fabricated such that its magnetization is free to rotate in response to an external magnetic field. Passing magnetic data bits on the magnetic disk of the hard disk drive cause rotation of the magnetization of the free magnetic layer which creates a change in the electrical resistance of the sensor, and an electrical sense current that passes through the free magnetic layer is correspondingly altered by the altering resistance of the free magnetic layer. The hard bias element provides a biasing magnetic field for stabilizing the magnetic field of the free magnetic layer, and in order to function properly the magnetic field of the hard bias element is formed from a high coercivity material where its magnetization is oriented in the track width direction of the read head.
In modern magnetic heads, the size of the magnetoresistive sensor is constantly being reduced to read ever smaller data bits on hard disks having greater areal data storage density. The size of the hard bias elements is likewise reduced. This can create difficulty in fabricating the necessary hard bias magnetic field, as the number of magnetic grains within the hard bias layer material are reduced where its size is reduced.
The problem in current magnetic heads is that the size of the hard bias elements is being reduced to the point that fewer than ten hard bias grains exist at the junction with the free magnetic layer. As a result, an off-axis orientation of the magnetic field of just one or two magnetic grains within the hard bias element can significantly impact the uniformity of the hard bias magnetic field, and this results in the creation of noise in the magnetic head signal. The present invention seeks to solve this problem by creating more magnetic grains within the hard bias element to create a more uniform biasing magnetic field for the free magnetic layer.